diff --git a/src/gerbil/runtime/util.ss b/src/gerbil/runtime/util.ss
index 071650b73..c8d166cdf 100644
--- a/src/gerbil/runtime/util.ss
+++ b/src/gerbil/runtime/util.ss
@@ -755,11 +755,8 @@ namespace: #f
 
 (def (write-u8vector (bytes : :u8vector)
                      (port  :~ output-port? :- :port)
-                     (start :~ (in-range? 0 (max 1 (u8vector-length bytes)))
-			    :- :fixnum
-                            := 0)
-                     (end   :~ (in-range-inclusive? start (u8vector-length bytes))
-			    :- :fixnum
+                     (start :- :fixnum := 0)
+                     (end   :~ (in-range-inclusive? start (u8vector-length bytes)) :- :fixnum
                             := (u8vector-length bytes)))
   => :void
   (:- (##write-subu8vector bytes start end port)